The invention relates to the construction of duct from ductwork pieces that have been formed with interlocking edge configurations. The common present practice is to form individual ductwork pieces at a factory site, and then using air hammers or other hand tools, assemble the ductwork pieces together by effecting interlocking of cooperating edge configurations thereof to form a completed duct. Such hand assembly can be time consuming and inefficient, and when assembly is made at a factory site, only relatively small amounts of material can be transported to the job site in each truck load since the trucks carry mostly air when they are transporting the completed ducts. There have been proposals (see U.S. Pat. No. 3,636,903 for example) for the automatic formation of straight duct, however such proposals require relatively large and complicated machines which are not readily adaptable to produce duct of different sizes, and are incapable of producing transition pieces.
According to the present invention, a method is provided which allow the automatic assembly of straight duct of all different sizes, and additionally allow the formation of transition pieces. According to one aspect of the present invention, duct work pieces may be formed at the factory site with the necessary edge configurations and transported in low volume configurations to the job site where they may be automatically assembled by a portable machine at the job site, the machine being simple to operate and susceptible of operation by only one or two operators. It is believed that the method and apparatus according to the present invention can result in significant time savings in duct assembly compared to the prior art while still being capable of assembly of a wide variety of duct sizes (including transition pieces), and can result in significant energy gains when the duct is transported to the job site in a low volume configuration.
According to one aspect of the present invention there is provided a method for forming a duct using an edge interlocking machine having rollers comprising the steps of: forming a plurality of ductwork pieces, each having a predetermined length, out of sheet material; forming at least one of the pieces so that it has an edge configuration adapted to be acted upon to interlock and form a seam with another piece to form the duct; feeding the plurality of pieces into the edge interlocking machine; and acting upon the at least one edge configuration so that it forms a seam with another piece to form a duct having the predetermined lengths. The edge configuration preferably is a Pittsburgh edge configuration, although a snap lock may be employed. A completed duct can be assembled from 2, 3, or 4 pieces. According to another aspect of the present invention, a method of forming ductwork for installation in a building at a job site is provided which uses a portable fabrication machine. The method comprises the steps of: forming duct work pieces out of sheet material, including forming at least one of the pieces so that it has an edge configuration adapted to interlock and form a seam with another piece to form a duct; transporting the ductwork pieces in an unassembled, low volume configuration to the job site; and interlocking the edge configurations of at least two of the pieces of ductwork to form a seam of a completed duct by operating on the pieces with the portable fabrication machine at the job site.
It is a primary object of the present invention to provide a method and apparatus for automatic assembly of duct from ductwork pieces. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.